Method of manufacture of adhfsive tapes



so that it maintains Patented Nov. 20, 1945 UNI ED STATES PATENT orriceMETHbD OF OF ADHESIVE TAPES Frank J. Tone, Niagara Falls,

andired Brown,

man, Kenmore,

Osborne L. Mall!- Niagara Fa Niagara Falls, N. Y.,

No Drawing.

Serial No. 148,104.

tion September 25, 19

Original application Divided and 41, Serial N June 14, 1937, thisapplica- Claims. (01.117-122) Thi invention relates to adhesive tapesand methods of manufacturing the same. More speciiically, the inventionis directed to improvements in tapes which are normall re-usable byreason of the character of the adhesive employed and the unification ofthe adhesive to the supporting backing material.

The present application is a division of our copending application,Serial No. 148,104, filed June 14, 1937. The adhesive tapes of ourinvention are .applicable to a number of uses such as in the painting ofautomobile bodies where it is desirable to protect certain parts of thesurfaces from the paint which is being sprayed on, for'use in surgery01: other similar purposes where the usual surgical tape is employed,for electrical purposes in place of the well-known electrical tapes andin general, for the purposes for which tapes of this character arecommonly used. a

It is desirable in tapes of this kind that the adhesive which is usedshall be sufliciently strong its unity when the tape is removed from theobject on which it is placed, that the adhesive be sufficiently tacky sothat the tape can be made to adhere to non-adhering surfaces by merelypressing it against such surfaces, and that the cohesion between theadhesive and the backing of the tape be greater than the ad hesion ofthe adhesive to the surface being coated. In such case, the tape can beeasily applied by merely laying it on the surface and rubbing lightlyand yet it can be removed as a unit by pulling and stripping it from thesurface. Adhesives which are permanently tacky and adapted to be made tostick to surfaces by the application of pressure alone are a tly called"pressuresensitive adhesives." Q

Where the tape is to be used to protect surfaces from lacquer or paint,it is necessary that the surface of the tape which is exposed when thetape is in place, be resistant to the action of the solvents employed inso that the tape will not be affected by the lacquer which is sprayedagainst it.

Heretofore tapes of this character have been made which include speciallprepared paper as, for example, in accordance with Re. Patent 19,128. Inorder tov make such tapes which will be satisfactory, it' is necessaryto employ a considerable number of steps. In the first place, the papermust be specially treated to unify it so that the individual fibres ofthe paper will not be stripped off and adhere to the adhesive surfacewhen the tape is unrolled. In order to the lacquer or the point obtain aunification of the adhesive with the treated paper, it is necessary tofirst coat a surface of the paper with a highly adhesive material sothat the coating of adhesive which is to be subsequently applied will bestrongly adherent to the coated side of the paper. And finally, it isnecessary to treat the back of the paper with a special material whichfurther unifies the fibres of the paper and also assists in the removalof the adhesive from the back of the paper when the tape is wound into aroll. Where the tape is to be use for masking purposes it is alsodesirable tha the paper be crinkled or creped so as to permit ofsumcient distortion to allow ad- Justment of the tape to curvedsurfaces.

We have discovered that very excellent adhesive tapes can beprepared ina mu h simplified manner by the use of special kinds of backings and byemploying new methods which we have invented. a

The backing materials which we have found to be especially suited forthe preparation of our tapes include a number of materials which arebroadly classifiable under the term plastics." By plastics we meanmaterials which are capabio of being put into solution with solvents andwhich deposit from such solvents films having a requisite strength andother properties which are desired in adhesive tapes. For example, wehave found it to be desirable in making tapes which are to be used asso-called "masking tapes" for use in protecting surfaces againstlacquer, to employ plastic materials which are adapted to be stretchedto some extent so that the tape will be made to conform to curvedsurfaces.

Among the materials which we have be suited for use in our improvedtapes are rubher, which may be vulcanized, dispersions of rubber in waxymaterials, modified rubbers or rubbers made by reacting crude rubberwith various chemicals, and certain film-forming resinssuch as theacetals or partial acetals of polymerized vinyl esters. I

Our invention includes a number of variations of a method which we havefound to be especially well adapted for the preparation of tapeemploying plastic materials as the backing. Generally speaking, themethod includes the step of unifying the backing material with theadhesive material by either and the backing, by employing aliquid whichis a solvent for both the adhesive and the plastic material, or by acombination of these steps.

In carrying out one form of our invention, we

found to heating films of the adhesive In place of the cumaron which mayhave a somewhat roughened or creped surface to make the surface of theadhesive irregular, onto which we coat a pressure-sensitive adhesive. Wethen apply a backing material to the exposed surface of the adhesive andcause a unification of the adhesive with the backing by any of themethods Just described, and then strip the tape thus formed from thesupporting web, after removal of the solvent if the films are formedfrom solutions. The supporting web may be of any suitable material suchas a well-sized cloth or paper or even metal. The adhesive may be any ofthe well-known materials and specifically, it may comprise rubber, asuitable resin, and zinc oxide as described in Example A of the Re.Patent 19,128.

Alternatively the backing may be applied first to the supporting web andthe adhesive subsequently applied, an intermediate and highly adhesivelayer being interposed between the backing and the pressure-sensitiveadhesive according to either method, if this is considered to bedesirable.

The backing material may be applied to the adhesive in the form of apre-formed film or alternatively, the plastic material which is to formthe backing may be dissolved in a suitable solvent and coated onto theadhesive by any suitable method such as by transferring it from a rollwhich is caused to rotate in a vat of the solution.

Alternatively, the backing material may be formed into a film and thencoated with the adhesive which has been put into solution in a solventwhich is or which contains a solvent for the backing material. Where thebacking is strongly attacked by the solvent, it is desirable that it besupported on a web until such time as the solvent has been removed andthe backing has again become strong enough to be self-supporting.

An alternative method of forming our improved tapes comprises theseparate preparation of webs of the adhesive and of the backing materialand the subsequent unification of these two films. Unification may bebrought about by wetting the surface of either or both of the films soas to bring about a mutual solution when the films are joined in thepresence of the solvent, followed by the subsequent removal of thesolvent. Alternatively, the films of adhesive and of backing materialmay be brought together while either or both of them are heatedto thepoint where they become sufilciently plastic so that unification isbrought about when the films are joined.

As set forth above the adhesive employed may be any one of thewell-known materials, and specifically it may be of resin described inExample A of the Re. Patent composed of the following ingredients:

Pounds Plasticized, first quality plantation rubber such as clear crepeor smoked sheets Cumaron gum or resin 2 Zinc oxide pigment 1 gum orresin, which is preferably an artificial resinous material coming underthe group name of cumaron and indene resins, there may be employed a lowboiling point natural resin as, for instance Burgundy pitch or pine oilfoots. The above ingredients are compounded on a rubber rolling mill toa plastic condition and then cut to desired body or consistency with arubber solvent such as benz'ol or a pctroleum solvent such as high testgasoline.

19,128. Such adhesive is The solutions of adhesives composed of rubberand resin such as that given specifically above, when made of aconsistency or viscosity such that they are capable of being appliedto'form films of suitable thickness, are commonly very sticky andstringy and accordingly are difilcult to apply in coatings of uniformthickness. We have found that this difiiculty with such solutions can beovercome by first forming such solutions preferably of a viscosityhigher than would normally be used if the solution itself were to beemployed as the coating material, and then dispersing in such solution asmall amount of water with the aid of a suitable dispersing agent. Suchdispersion's, when suitably made, are not at all stringy and sticky, butare rather of a buttery consistency so that they can be very readilysmoothed out much in the manner in which a soft butter can be spread. Inpreparing such dispersions, we employ a dispersing agent which issoluble in a solvent but insoluble in water. By incorporating such adispersing agent in a solution of adhesive and then adding smallquantities of water and agitating as by rapid stirring, the water iscaused to disperse through the mass of solution andappears to break upthe solution and form the buttery consistency which we have deingsincluding paper and cloth as well asthe plastic materials of ourinvention.

One particular material which we havejound to be especially well suitedfor use in our masking tapes comprises the product described and claimedin the patent to Abrams et al. No. 2,054,112. These compositionscomprise rubber and a waxy material, specifically paraffin wax. They maybe employed either as the backing material or as the adhesive materialor for both purposes by choosing suitable proportions of the wax andrubber and by adding a suitable tack-producing agent such as resin oroil to the adhesive composition. well-adapted for the production ofadhesive tapes by the method where the adhesive and the backing areJoined and unified by the use of heat.'

Films of the compositions can be prepared in accordance with Patent No.2,054,114, two separate films being made and brought together while inthe heated condition so as to obtain the desired unification of theadhesive to the backing. Such tapes have been found to be well suitedfor many purposes and in addition we have successfully prepared tapes byemploying the rubber and wax composition as the backing material andcoating films of such material with the rubber-resin-zinc oxide adhesivewhich is more conventionally employed in tapes of this character.

Where the tapes are to be employed for masking purposes, the solvent forthe lacquer tends to soften these rubber-wax compositions and it isaccordingly desirable that the back of the tape be coated to protect itfrom attack by the SOIVCllta used in lacquers. One method which we havesuccessfully employed for overcoming this dimculty comprises firstforming the tape by any of Such compositions are especially comprisesuch materials as the acetaldehyde acetal of polyvinyl acetate,fiexibilized by the addition of about 5% of a suitable plasticizingagent such as tricresyl phosphate. These resins are soluble in lacquersolvents and one method which we have used to protect them againstattack by such solvents comprises applying a film of an aluminum varnishwhich comprises finely puiverized aluminum suspended in an oil basevarnish. Upon oxidation of the oil the thus-formed film is renderedhighly resistantto the action of lacquer solvents. Alternatively, thebackings may be protected against attack by such solvents by applying tothem, while they are still liquid and adhesive, a thin layer ofprotective material such as powdered aluminum, very finely pulverizedwood flour, or the finely divided cellulosic material commonly known asalpha flock.

While we have described our invention by reference to certainembodiments, the invention is susceptible to various modifications suchas the inclusion of medicants in tape for use for surgical purposes, theemployment of highly adhesive films intermediate between the backing andthe pressure-sensitive adhesive, or of protective films on the uncoatedside of the backing. Such modifications and other obvious alterations inthe structure as well as other methods and materials may be employedwtihout departing from the spirit of the invention, the scope of whichis set forth in the appended claims.

We claim:

1. In a method of making adhesive tape, the

steps which comprise making a rather stifl! and viscous solution of apressure-sensitive adhesive mixture comprising rubber, a resin, and zincoxide in a non-aqueous solvent, adding to said solution a smallpercentage of a water-in-oil type dispersmg agent which is insoluble inwater but soluble in the said non-aqueous'solvent, dispersing about 24%of water in the said solution to form a water-in-oil type dispersionhaving the smoothspreading property characteristic of a soft butter,spreading said dispersion on a backing, and re moving the water andsolvent from the dispersion. 2. In a method of making adhesive tape, the

steps which comprise making a rather stifi and viscous solution ingasoline of a mixture comprising rubber, coumarone resin, zinc oxide,and a small percentage of a water-in-oil type dispersing agent selectedfrom the group consisting of diglycol laurate and calcium resinate,dispersing a small percentage of water through the adhesive solutionwith the water in the dispersed phase, spreading the dispersion thusformed on a backing, and removing the water and solvent from thedispersion, said dispersion having the smoothspreading propertycharacteristic of a soft butter. 3. In a method of making adhesive tape,the steps which comprise making arather stiff and viscous solution of arubber-base pressure-sensitive adhesive in a non-aqueous solvent, addingto said solution a small percentage of a water-in-oll type dispersingagent which is insoluble in water but soluble in the said non-aqueoussolvent, dispersing about 2-4% of water in the said solution to form adispersion having the smooth-spreading property characteristic of a softbutter, spreading said dispersion on a backing, and removing the waterand solvent from the dispersion.

4. In a method of making adhesive tape, the steps which comprise makinga dispersion having the consistency and smooth-spreading propertycharacteristic of a soft butter and comprising approximately 2-4% ofwater dispersed through a rather stiff and viscous solution of apressuresensitive adhesive containing approximately 1-2% of awater-in-oil type dispersing agent, spreading the said dispersion on abacking, and removing the water and solvent from the dispersion, saidadhesive comprising a rubber compound and a resinoustackiness-augmenting agent.

5. In a method of making adhesive tape, the steps which comprise makinga dispersion having the consistency and smooth-spreading propertycharacteristic of a soft butter and comprising approximately- 2-4% ofwater dispersed through a rather stiff and viscous solution of anadhesive which is permanently tacky and adapted to be made to stick tosurfaces by the application of pressure alone and containingapproximately 1-2% of diglycol laurate, spreading the said dispersion ona backing, and removing the water and solvent from the dispersion, saidadhesive comprising a rubber compound and a resinoustacklness-augmenting agent.

FRANK J. TONE. OSBORNE L. MAI-IIMAN. FRED BROWN.

